This invention relates to a cable closure, by means of which environmental protection may be provided around a cable splice, termination or other cable portion. The invention may be used with power cables, CATV cables or telephony or other communications cables. The invention is likely to find most use in protecting splices in, and terminations of, optical fibre cables.
The use of closures for environmental sealing of cable splices is of course well known. Cables are produced in finite lengths and therefore lengths of cable frequently need to be joined together. The function of a closure is to provide a seal that bridges the jackets of the spliced cables. A closure may also provide other functions in addition to environmental protection, such as mechanical protection and axial-pull strength. Closures may be used around simple end-to-end splices between cables, but frequently more complex splices require sealing. For example, a large cable containing many conductors (by which term I include optical fibres as well as electrical conductors) may be split into two or more smaller cables. Ultimately, a cable will be effectively terminated where it is broken down to single conductors or small groups of conductors. Such terminations also require cable closures to protect them.
It is frequently necessary to install a cable closure around a cable splice (or termination) where access to ends of the cables is not available. In such circumstances the closure clearly cannot be permanently of closed cross-section: the closure needs to be xe2x80x9cwrapped aroundxe2x80x9d the cables, rather than slid onto the cables from one end. This term xe2x80x9cwrap aroundxe2x80x9d derives from cable closures that were formed from flexible sleeves or longitudinally-slit tubes. It is, however, a general term that merely refers to the capability of installation around a cable at some point between its ends. Thus, the term includes substantially rigid half shells that are assembled around the splice. The shells may be hinged or otherwise linked together by moulded-in strips or by tapes or living hinges etc. The term xe2x80x9chalf shellsxe2x80x9d does not imply any particular shape, and the two half shells may be different or generally similar in shape to one another. Thus, each half shell will have a periphery that abuts the periphery of the other half shell, and each will have a hollow body portion, roughly semi-circular in cross-section, so that when the two half shells are brought together they define a roughly rectangular or circular cylindrical enclosed space within which the splice will lie. Half shells may, however, differ from one another, so that one might be described as a base plate, and the other as a cover. These terms xe2x80x9cwrap aroundxe2x80x9d and xe2x80x9chalf shellsxe2x80x9d are well-known in the art.
Many cable closures have been proposed that make use of half shells. Unfortunately, many problems remain. The performance requirements of a closure are very difficult to meet. The problem arises largely because a closure must be very quick and easy to install, usually with unskilled labour, and under difficult conditions, but must meet very stringent performance specifications. As a general rule a cable closure is expected to have a life time comparable to that of the cables which it protects, typically twenty or more years. Cables are generally situated out of doors and are subjected to extremes of temperature and humidity. Various tests have been devised to mirror this long-term performance. Although different tests are applicable to different cables in different situations, typical tests involve pressurisation of the closure whilst it is subjected to temperature cycling, often under wet or humid conditions. A closure is expected not to leak for a certain number of such cycles. Clearly, closures of the half shell design start out at a disadvantage because a seal must be provided between the half shells as well as between the incoming and outgoing cables and each half shell. A particularly severe problem arises at the region where a seal between the half shells meets a seal between the cables and each half shell. This region is known as the xe2x80x9ctriple pointxe2x80x9d. It can therefore be seen that design of such a closure is a difficult matter.
The difficulties are, as usual, increased by the need for low cost. The requirement for low cost means that it is not possible to supply different designs of closure for each cable size and for each splice or termination configuration. Thus, a single design of closure must be able to accommodate, for example, a simple in-line splice between two cables, a butt splice between two cables (where the two cables lie side-by-side), and various configurations, such as xe2x80x9cone in-two outxe2x80x9d where one cable enters one end of a closure and two leave at an opposite end. In order to accommodate a range of splice configurations, one may decide to provide a closure that has four cables seals, two at each end. Cable seals are, unfortunately, expensive and such a closure would need to be provided with four such seals. Each of these seals would need to be capable, not only of sealing to an incoming cable, but also be capable of being closed in case the full compliment of cables was not to be employed. The present invention provides a particularly simple and elegant solution to these problems.
Before the invention is described in detail it may be worth noting some prior art closures of the half shell type. U.S. Pat. No. 5,322,973 discloses an aerial closure for protecting a cable splice. It has a central header portion and wing-like housing segments that may enclose the splice. The wing-like housing segments may be raised to provide access to the splice. Each end of the closure has a seal assembly for sealingly engaging the ends of the incoming cables. These assemblies have concentrically circular and corrugated features thereon so that an appropriately size hole may be cut to allow entry of 1, 2 or 3 cables of various sizes.
U.S. Pat. No. 4,805,979 discloses a fibre optic splice closure comprising a base to which a cable may be anchored, and a cover which overlies the base. Seals are provided around the cables at the position where the base meets the cover.
U.S. Pat. No. 4,492,816 discloses half shells for forming a cable splice. Half shells have flanges which abut one another in the assembled configuration. The adjacent flanges define a duct into which sealing material in the form of a paste may be introduced. Opposite ends of the resulting closure are provided with jaws which clamp against the incoming cables. Two jaws define between them a chamber which communicates with the sealing duct by means of a channel formed around the entire periphery of a jaw adjacent to the chamber.
EP 0543350 discloses a cable enclosure formed from a base and a cover which are secured together by bolts through flanged portions thereof. Various cable guide sections are located at the interface between the base and the cover.
GB 1260273 discloses a housing for electrical connections, which comprises a cylindrical central part and end parts that form a seal between the central housing and each incoming cable. The end parts are moulded to provide a number of cable entry ports. The ports are initially blind. The extreme ends of the ports are cut off as and when required to allow cables to pass through. The ports are heat-shrinkable so that after insertion of a cable a port can be shrunk to make sealing contact with it.
U.S. Pat. No. 5,109,467 discloses an optical fibre interconnect cabinet in the form of a box with a lid. The side walls of the box are provided with slots which can receive removable blanks. With the blanks in place, and the lid closed, the box is sealed. With the lid open, a blank can be removed to provide a port for cable entry.
Whilst each of those prior art designs provides some of the benefits that I now seek, each unfortunately suffers from one or more problems. For example, some of the designs are not fully xe2x80x9cwraparoundxe2x80x9d, some are not suited for environmental protection out of doors, some are too complex and expensive, and some do not provide the desired flexibility in terms of cable size and/or cable configuration.
I have now designed a cable closure that can provide excellent sealing for a variety of cable configurations, and which allows quick and simple installation.
Thus, the invention provides a cable closure comprising:
1) two half shells that together form an enclosed space for housing a cable (more particularly some part of a cable such as a termination or splice),
2) a sealing strip (preferably formed of a resilient material such as a rubber or a synthetic elastomer) positioned between a peripheral region of each half shell such that, when the half shell are brought together, said space can be sealed;
3) at least one of the shells having a removable portion that, when removed, provides a cable entry port between the two shells, the sealing strip providing a seal between that portion and the other shell (preferably a removable portion of the other shell when, as is preferred, each shell is provided with a removable portion).
The invention also provides a method of enclosing a cable, which comprises:
a) providing a cable closure as defined above;
b) removing said removable portion;
c) removing that part of the sealing strip that provided a seal between said removable portion and said other shell; and
d) bringing the half shells together around the cable such that a cable passes through the port provided by removal of the removable portion.
One of the half shells may have the form of a base and the other the form of a cover, or each half shell may have a generally hollow region which together form said space. Thus, each half shell may be, for example, substantially semi-circular, semi-rectangular or semi-elliptical, in cross-section such that when the half shells are brought together a generally cylindrical space is formed that is substantially circular, substantially rectangular particularly with rounded corners or substantially elliptical in cross section. In general it will be a desirable for each half shell to be formed, for example by moulding, from a single piece of material. Each half shell may, however, comprise two or more parts joined together, but this has the disadvantage that seals between those parts must be provided.
Where I refer to the sealing strip being positioned between xe2x80x9cperipheralxe2x80x9d regions of the half shells I simply mean that the sealing strip is towards the outside of the shells, although it need not of course be at the extreme edge. In general, the sealing strip will lie between peripheral flanges or edge walls of the half shells, which flanges or edge walls may extend outwardly of the sealing strip for example to provide means by which the half shells can be held together. Such means may comprise a bolt that passes through holes in the flanges or edge walls. It will be understood that it is desirable that such holes be provided outwardly of the sealing strip since otherwise a leak path into the splice case could exist via the holes.
I refer above to the space within the closure being capable of being sealed when the shells are brought together. This is because some additional sealing means or sealing operation may be required. However, in general, sealing between the half shells will result directly from the half shells being brought together with the sealing strip between them, although some fixing means such as the bolts mentioned above may be required to prevent the half shells from separating particularly if the closure is to be pressurised. Thus, the sealing strip preferably follows a substantially closed path around the periphery of the half shells. The sealing strip is preferably in one piece along its length, and may be continuous.
Complete sealing of the space within the closure will of course usually require some additional seal to be provided between incoming cables and the ports through which they enter. In general, a cable sealing device will be provided that is of annular shape, the outside surface of the annulus sealing against the internal surface of the port, and the inner surface of the annulus sealing against the external surface of the cable. Thus, the cable sealing device effectively fills any gap between the cable and the port through which it enters. The design of such cable sealing devices presents its own difficulties. These difficulties result in part from the need to be able to seal to cables of different sizes, since there will be some size variation even between cables of one nominally standard size. Furthermore, the cable sealing device needs to seal not only to the cable and to the surrounding half shells (where they define the port), but also to the sealing strip. This is the xe2x80x9ctriple pointxe2x80x9d problem referred to above. The cable closure of the invention is able to overcome this problem in a particularly elegant way. Thus, I prefer that at least one of the half shells (preferably both) is shaped to define, adjacent and inwardly of the port, a chamber for receiving a cable sealing device; and that the sealing strip run along opposed longitudinal sides of said chamber such that, when the sealing device is in the chamber, the strip at each said side contacts each half shell and the cable sealing device.
In preferred designs of the closure at least two said removable portions are provided side-by-side. A particularly preferred closure is designed to provide four cable entry ports, two side-by-side at each end. The closure may be supplied to the customer with one (or more) ports already open, that is with one (or more) potential removable portions being absent. The precise design will of course depend on the cable configurations possessed by the customer. Therefore, I prefer the closure to have at least two side-by-side ports, whether or not both of the ports in question have removable portions that would close them. I prefer that at least one of the half shells be shaped to define adjacently inwardly of each said port a chamber for receiving a cable sealing device; and that the sealing strip run along opposed longitudinal sides of each chamber such that, when a sealing device is in each chamber, the sealing strip at each said side contacts each half shell and the respective sealing device; and that separate portions of the sealing strip run between the chambers along each of the adjacent longitudinal sides. An alternative is possible; it would be possible for a single portion of sealing strip to run between the two side-by-side chambers. That single portion would therefore be shared by the two chambers.
That alternative arrangement is, however, less satisfactory because it would need to be rather wide, or the two chambers to be rather close, if that single portion of sealing strip were to contact both sealing devices.
These separate portions of sealing strip are preferably joined together towards an inward end of the chambers. In that way the seal is completed. Also, such a design allows the two half shells to be joined together by the means of, for example, bolt that passes through holes in the half shells; the holes would be positioned between the separate portions of sealing strip and outwardly of the position at which they are joined. In this way, the holes for the bolt do not provide a leak path into the splice case.
I prefer that the removable portion that gives rise to the cable port be an integral part of a half shell, although it may initially be separate and later bonded or otherwise sealing fixed to the half shell. The port preferably is formed substantially equally in each half shell, and therefore each half shell preferably has a said removable portion, both of which are to be removed to define the port.
In order that the cable sealing device form a good seal to the half shells, I prefer that the chambers (which will usually be defined by the inside surfaces of each half shell) be wholly concave in cross-section. Clearly, any irregularities in the curvature of the chamber will make a reliable seal difficult. If the cable sealing device is to seal a single cable then the external surface of the sealing device will preferably be substantially circular. However, I prefer that each sealing device be capable of sealing at least two cables, more preferably two cables side-by-side. In this case the cable sealing device need not be of simple annular shape, but may have, say, the shape of two annuli side-by-side with the roughly triangular spaces between them filled in. Overall, in cross-section the cable sealing device may be substantially elliptical. However, a circular cross-section may still be appropriate, particularly if four cables are to be sealed. Clearly, the chambers for the sealing device should have a cross-section or shape that corresponds to the sealing device, and will in general therefore be substantially circular or substantially elliptical in cross-section. The chambers may be provided with some fixing means such as one or more lugs or flanges to prevent axial movement of the sealing device.
The cable sealing device may be of the general design and construction disclosed in WO 90/05401 (N. V. Raychem S. A.). Thus, the sealing device may comprise along an axis thereof first and second end parts and a sealing material between them, the first and second ends parts and the sealing material each allowing a cable to pass through them, the device having means to bring the first and second end parts together thereby putting the sealing material under compression axially, and causing it to be displaced radially to contact a cable therein and the chamber therearound. In general, the first and second ends parts and the sealing material will be provided with an axial hole through which the cable can pass. Also, the first and second end parts and the sealing material may be provided with a radial slit that extends from their outer surface to said hole, which slit can be opened out to allow the sealing device to be xe2x80x9cwrapped aroundxe2x80x9d the cable. A preformed hole need not be provided in the sealing material since it may be possible to rupture the sealing material by pushing the cable through it.
The means that bring the first and second end parts together may comprise a nut and a bolt, one of which is fixed to one end part and the other of which bears against the other end part such that when they are relatively rotated the parts move together. Resilient means such as a spring, preferably a coiled compression spring, may be provided to bias resiliently together the first and second parts, thus maintaining the sealing material under compression during the service life of the closure.
The sealing material preferably comprises a gel, but other materials such as rubbers or mastics may be used. A gel is a liquid-extended polymer composition preferably having a cone penetration value (measured by a modified version of ASTM D217) within the range from 30 to 400 (10xe2x88x921 mm), and an ultimate elongation (measured by ASTM D412) greater than 100%, and preferably also with substantially elastic deformation to the elongation of at least 100%. The composition may contain three-dimensional cross-linked molecular formations, or merely behave as if it contains such molecular formations.
Useful compositions may be provided comprising at least 500 preferably at least 1000 and preferable not more than 5000 parts by weight of an extender liquid per 100 parts by weight of block copolymer or other polymer. Preferred block copolymers are those based on styrene and olefines such as ethylene and butylene. Particularly useful gels may be made using styrene-ethylene-butylene-styrene block copolymers such as those marketed by Shell under the trade name xe2x80x9cKratonxe2x80x9d. Such gels are disclosed in WO 90/05401 referred to above.
The sealing strip may be made of any suitable material, particularly a resilient material such as a rubber or synthetic elastomer. Examples include solid or hollow rubber, rubber foam and rubber gel. Such materials may be used in combination with other materials, for example a mastic, gel or other sealant. In this way, one component may provide a resilient bias and another component may be more deformable and be used to make intimate contact with the various surfaces. For example, a strip (of any suitable cross-section) of resilient material may be positioned in a channel or groove in one or both of the half shells. If desired, a sealing strip may be positioned in each half shell so that the two sealing strips contact one another when the two half shells are brought together. I prefer that the sealing strip or strips be continuous lengthwise (before a part is removed after removal of the removable portions of the half shells) in the region of the removable parts and along the sides of the chambers adjacent those removable parts. More preferably I prefer that the sealing strip (or each strip if one is positioned initially in each half shell) be unbroken along its length for the whole closure. However, in certain circumstances it may be desirable to use separate strips at each end of the closure.